High-pressure evolution ofFe2O3electronic structure revealed by x-ray absorption

Abstract

We report the high-pressure measurement of the $\text{Fe}\text{ }K$ edge in hematite $({\text{Fe}}_{2}{\text{O}}_{3})$ by x-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as ${\text{Fe}}_{2}{\text{O}}_{3}$ transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal-field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced electronic phase transitions of ${\text{Fe}}_{2}{\text{O}}_{3}$ is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin transition pressure.